Certain types of buildings are provided with walls and roofs of transparent material in the form of glass or plastics in order to utilize the solar energy for heating the interior of the building in temperate climates. Such buildings are winter gardens, sun lounges or greenhouses.
Even in regions having a temperate climate, however, the solar energy may be so intense that the inside temperature of the building becomes undesirably high, and the building is then ventilated by opening at least one window, and in case a more intensive ventilation is called for by attempting to make a draught by opening windows located at two opposite sides of the building in order to take advantage of the difference in wind pressures. Another possibility is to utilize the differences of temperature inside the building by opening windows located at different heights, thereby taking advantage of the so-called chimney effect for ventilation of the building. In that case the windows may be provided either on a roof surface or in a wall, or in one wall, or in a first wall extending down from a roof surface, and a second wall extending down from the roof surface like a kind of chimney, which is particularly common in winter gardens built adjacent to a residential property.
It is well-known that the chimney effect is produced by the difference of density between cold and warm air, causing the warm air to rise and leave the building through the upper opening, whereas the rising warm air is replaced by colder air entering through the lower opening.
The above described effect is known for example from DE Printed Specification no. 1,008,517 and GB Patent Specification no. 1,352,622.
DE Printed Specification no. 1.008,517 describes a greenhouse, which is provided with openings at the bottom along the edge of one wall, which openings may be covered by flaps. In addition, the greenhouse has a ridge turret with openings, whereby the wind can blow horizontally through the ridge turret thereby producing an ejector effect, which may strengthen the chimney effect between the opening at the bottom along the edge of the greenhouse and the ridge turret.
GB Patent Specification 1,352,622 describes a greenhouse, which is provided with openings at the bottom along the edge of two opposite walls. These openings are fitted with sheet members, which are adapted to slide in vertical direction to open respectively close the openings, said openings being further provided with nozzles to spray water on the entering air in order to cool down the air by evaporation of the water and to increase the amount of steam and thus improve growth conditions for the plants in the greenhouse. Heated air can escape through openings in the roof. The flaps are slidable or can be controlled by means of a rack-and-pinion drive or with the aid of pneumatic cylinders, which may be activated by thermostats.
For rational operation greenhouses are usually very long, for example up to 100 meters. Using a rack-and-pinion drive to open and close the openings will result in considerable drawbacks, see for example DK Printed Specification no. 148,761, in view of the fact that the changing temperatures in the greenhouses on a day and night basis will cause the various shafts etc. to vary in length, requiring the provision of special measures in order to correct the engagement of the rack bars with other parts of the mechanism, thereby rendering these rack-and-pinion drives unduly expensive to use.
It is known to use activation means based upon a cylinder to open the windows of hotbeds or greenhouses, whereby the cylinder contains a fluid, which will expand or contract when heated respectively cooled, as a result of which a piston in the cylinder will move accordingly and thereby open or close the window openings, see for example DE Printed Specification no. 1,043,703.
The above mentioned specifications provide solutions, which are complicated and therefore unduly expensive to use, irrespective of whether they are to be used in very long greenhouses for cultivation of plants for commercial purposes, or whether they are to be used in a sun lounge or a winter garden comprising a few square meters only of a private residence.